How about a website where users can upload pictures (with description) of what they have available to trade, and other users can match the appropriate items fro

How about a website where users can upload pictures (with description) of what they have available to trade, and other users can match the appropriate items from their inventory to make trade offers. With the user's profile, you can have a trade history, feedback, the ability to make private trades (maybe a premium feature), and a "showroom" where users can display their prized widgets. Of course forums, private messaging, along with advertising would be appropriate. I've never built an online community, but I would wait to gauge interest of users interested in purchasing widget-related products before investing the time and capital to develop that.